Special Guest Stars David Ramsey as John Diggle Victor Garber as Dr. Martin Stein / Firestorm Stephen Amell as Oliver Queen / Arrow Emily Bett Rickards as Felicity Smoak Melissa Benoist as Supergirl / Kara Zor-El / Kara Danvers Brandon Routh as Ray Palmer / The Atom Dominic Purcell as Mick Rory Franz Drameh as Jefferson "Jax" Jackson / Firestorm Caity Lotz as Sara Lance / White Canary Willa Holland as Thea Queen / Speedy Guest Stars Audrey Marie Anderson as Lyla Michaels / Harbinger Donnelly Rhodes as Glasses Christina Brucato as Lily Stein Jerry Wasserman as President of the U.S.A. Co Starring Sonia Beeksma as News Reporter Linda Ko as NSA Official